Identification and Quantification of Pigments in Prickly Pear Fruit

E.M. Yahia and E. Castellanos C. Mondragon-Jacobo Facultad de Ciencias Naturales Instituto Nacional de Investigaciones Universidad Autonoma de Queretaro Forestales y Agricolas y Pecuarias Juriquilla, Queretaro, 76230 Campo Experimental Norte de Guanajuato Mexico Mexico

Keywords: Cactacea, Opuntia, , , , mass spectrometry

Abstract Identification and quantification of betalains in ten cultivars/lines of prickly pear (Opuntia spp.) fruit were conducted with reverse phase high-performance liquid chromatography-diode array detection (HPLC-DAD) coupled with electrospray mass spectrometry (ESI-MS). Betacyanins and betaxanthins were identified by comparison with the UV/Vis and mass spectrometric characteristics as well as the retention times of semi-synthesized reference betaxanthins. Carotenoids and were also identified and quantified based on their molecular mass determined by applying HPLC-DAD coupled with Positive Atmospheric Pressure Chemical Ionization Mass Spectrometry (APCI-MS). A total of 24 known/unknown betalains were present in the studied prickly pear fruit, including 18 betaxanthins and 6 betacyanins. The ratio and concentration of pigments are responsible for the color in the different cultivars, showing the highest betalains content in fruit of purple color, comparable to that found in red beet (Beta vulgaris L. ‘Pablo’). All cultivars/lines had a similar profile, in which lutein was the most abundant compound in ‘Camuesa’, while neoxanthin was the most abundant compound in ‘21441’. was the most abundant in all cultivars/lines with the highest quantity in ‘21441’. To our knowledge, this is the first time that separation of carotenoids and chlorophylls has been reported in cactus pear fruit using mass spectroscopy. Our results indicate that prickly pear fruit can be considered as a potential source of yellow and red natural colorants.

INTRODUCTION Prickly pear (Opuntia spp.) is a popular fruit in many countries (Puga, 2004; Yahia, 2009). Approximately 200 species are known in the world and Mexico possesses an extensive genetic variability, with a diversity of fruit pulp tonalities (red, white, yellow). Pigments have many important functions, such as imparting color, important for pollination, and have also been implicated in health related benefits (Stinzing et al., 2001). Chlorophylls and carotenoids are widely distributed in plants. Betalains are a water-soluble class of nitrogen-containing vacuolar pigments, and are generally classified into betacyanins and betaxanthins (Stinzing et al., 2005). They are found in Beta vulgaris (family Chenopodiaceae), amaranth seeds (Amaranthaceae), Bougainvillaea bracts (Nyctaginaceae), and flowers or other plant parts within the Aizoaceae, Basellaceae, Didieraceae, Phytolaccaceae and Portulaceae. The objective of this study was to identify and quantify chlorophylls, carotenoids and betalains in the fruit of ten Mexican prickly pear cultivars and lines, by using high-performance liquid chromatography and Time-of- Flight mass spectrometry.

MATERIALS AND METHODS Ten cultivars and lines of prickly pear with fruit of purple, red, orange, yellow, and white pulp colors were selected for this study. The cultivars were ‘Camuesa’ (O. robusta Wendl.), ‘Roja Pelota’ (O. ficus-indica (L.) Mill.), ‘Cardona’ (O. Streptacantha), ‘Liria’ (Opuntia sp.), ‘Roja Lisa’ (O. ficus-indica (L.) Mill.), ‘Naranjona’ (V. Apastillada), ‘Reyna’ (O. Amyclaea), and the lines were ‘2651’, ‘21441’ and ‘2142’. After manual peeling and removal of the seeds, fruit pulp was freeze-dried, and the

th Proc. 6 International Postharvest Symposium Eds.: M. Erkan and U. Aksoy 1129 Acta Hort. 877, ISHS 2010 resulting dried powder was stored in the dark at -20°C until pigment extraction and analysis. For pigments extraction, dry fruit tissue was stirred for 10 min in darkness in 10 ml of MTBE and 1% BTH, MeOH (9:1) or hexanes-acetone-EtOH (2:1:1) as solvents (for chlorphylls and carotenoids), or in a citrate-phosphate buffer (pH 6.5) and water (20 ml) as solvents (for betalaines). After they were stirred, the samples were centrifuged at 12000 g at 15°C for 15 min. Supernatants were filtered through a 0.45 µm pore size white nylon filter, and the extracts obtained were analyzed spectrophotometrically and by HPLC. was extracted for the partial synthesis of betaxanthin standards from the fresh roots of red beet (Beta vulgaris L. ssp. ‘Pablo’). For chlorphylls all determinations were performed using a UV/Vis Beckman spectrometer equipped with UVWinLab V 2.85.04 software. Measurements were performed in triplicate, and chlorophyll content (mg/cm2) was calculated from espectrophotometric measurements at 645 and 663 nm. Identification of carotenoids by HPLC-DAD analysis was performed using an Agilent HPLC series 1100 equipped with ChemStation software, a G1322A degasser, a G1311A quaternary pumps, a G1316A column oven, and a G1315A diode array detector coupled to a 6210 time-of-flight (TOF) mass spectrometer equipped with an APCI ionization source, and Mass Hunter manager software (A.02.01). The UV/Vis spectra were obtained between 200 and 700 nm, and the chromatograms were processed at 450, 436, 663 nm for carotenoids and chlorophylls identification. The mass spectrometry parameters were as follows: positive mode; dry gas temperature, 350°C; flow, 5 L/min; nebulizer 20 psi, capillary voltage, 4000. The mass spectra were obtained with scan range of m/z from 100-1000. Carotenoids separation was carried out using analytical scale C30 reversed-phase column (150×4.6 mm i.d., 3.0 μm), with a C30 guard column (20×4.6 mm i.d), operated at 15°C. The carotenoids composition of the different extracts was studied using MeOH (eluent A) and MTBE (eluent B) mixture. Carotenoids were separated starting with isocratic condition: 0%B for 10 min, followed by a linear gradient from 0%B to 100%B within 30 min, before re-equilibration to the starting conditions. The flow rate was 1.0 ml/min, and the injection volume for all extract samples was 50 μl. Not all standards were available to us and therefore only the identity of the lutein chromatographic peak could be confirmed by their comparison of visible spectral characteristics or retention times. Identification of the carotenoids and chlorophylls had to be confirmed by mass spectrometry. The lutein and neoxanthin carotenoids were quantified by HPLC, using lutein as a standard. For the quantification of betalains all determinations were performed in a UV-vis spectrometer equipped with UVWinLab V 2.85.04 software. The pigments were extracted using two solvents, McIlvaine buffer (pH 6.5, citrate-phosphate) and water. The UV-vis absorption spectra were recorded to obtain absorption values of 0.9≤ to ≤1.1 at their respective absorption maxima. Measurements were performed in triplicate, and the betalain content (BC) was calculated according to literature with a slight modification. In all cases, water extracted the highest level of pigments. Identification of betalains by HPLC-DAD analysis was performed in an Agilent HPLC series 1100 equipped with ChemStation software, a G1322A degasser, a G1311A quaternary pumps, a G1316A column oven, and a G1315A diode array detector. Analyses were performed using an analytical-scale (150×4.6 mm i.d.) symmetry C18 reversed phase column with a particle size of 3.5 μm, operating at a flow rate of 1 ml/min and a temperature of 25°C. The betaxanthin and betacyanin composition of differently colored extracts were studied using water (eluent A) and methanol (eluent B) mixture. Betalains were separated starting isocratically with 100% A for 10 min followed by a linear gradient from 0% B to 30% B for 30 min, and finally a linear gradient from 30% B to 100% B for 20 min, before re-equilibration to the starting conditions. The injection volume for all extract samples was 20 μl. Betaxanthins and betacyanins were monitored at 482 and 535 nm, respectively. The identities of the different chromatographic peaks were

1130 confirmed by their visible spectral characteristics in comparison with standards and retention times. HPLC-DAD was coupled to a 6210 time-of-flight (TOF) mass spectrometer equipped with an ESI source, Mass Hunter manager software (A.02.01), operating in the positive ionization mode. Nitrogen was used as the dry gas at a flow rate of 12 L/min and nebulizing (35 psi). The spectra were taken in the presence of formic acid to promote [M+H]+ ion production (electrospray voltage 3.5 kV), nebulizer temperature was set at 350°C. The betaxanthin and betacyanin compositions of different colored extracts were studied with 1% formic acid in water (v/v, eluent A) and methanol (eluent B) mixture. Betalains were separated starting isocratically with 100% A, followed by a linear gradient from 0% B to 10% B in 20 min, and then a linear gradient from 10% B to 30% B in 10 min, and finally a linear gradient from 30% B to 100% B in 5 min before re-equilibration to the starting conditions. The injection volume for all extract samples was 20 μl. For the identification of the yellow betaxanthins, semi-synthetic standards had to be synthesized and structures had to be confirmed by mass spectrometry. Betaxanthin reference compounds were synthesized by modified partial synthesis according to a method described previously. Betanin powder (10 mg) was hydrolyzed in 1 ml NH4OH (pH 11) for 45 min, hydrolysis was controlled spectrophotometrically at 420 nm to obtain betalamic acid, and amino acid or amine was added to the alkaline solution of betalamic acid in a 10-fold molar excess. After vortixing, condensation was allowed for 20 min to yield the respective betaxanthin which was freeze-dried and the yellow crude semi-synthetic standards were kept frozen (-20°C) in the dark until analysis.

RESULTS AND DISCUSSION We have used several solvent systems for carotenoids analysis; the best results were obtained when the system described above (MeOH/MTBE) was used. Other methods for carotenoids analysis by HPLC have been reported; most of them use a solvent mixture of three components, MeOH, MTBE and water. The carotenoids pattern was dominated by lutein and the neoxanthin as the principal carotenoid pigments, while chlorophyll a was the principal pigment of chlorophylls group in all cultivars/lines (Table 1). Fruit of ‘Camuesa’ showed an additional compound at around 24.5 min which is not present in the other cultivars and also have the lowest level of chlorophyll a. In spite of the fact that ß- has been reported in fruit of prickly pear, it was not detected in our study in any cultivars or lines. Table 1 shows the partial identification and quantification of each compound present in the chromatographic pattern, and peak assignment of the lypophilic extract of the ten prickly pear cultivars/lines for carotenoids and chlorophylls pigments monitored at 450, 436 and 663 nm, respectively. The identity of these compounds was confirmed by HPLC coupled with mass spectrometry provided molecular mass and structural information. Table 2 shows the diverse variation in the content of total chlorophyll, chlorophyll a and b in the 10 cultivars and lines. Water extracted the highest amount of betalaines (Tables 3 and 4), and the highest betacyanin content was found in ‘Camuesa’, followed by ‘Roja Pelota’, ‘Cardona’, and ‘2142’, with the lowest contents found in ‘Reyna’. The betaxanthins content in these three cultivars was much higher than in the yellow cultivars. Other cultivars such as ‘2142’, ‘Liria’ and ‘Roja Lisa’ showed less content but still the betacyanins contents are higher than in the other cultivars. On the other hand, yellow cultivars such as ‘Naranjona’, ‘2651’, ‘21441’ had higher betaxhantins levels than betacianins content. Thus, the quantitative determinations demonstrated that the different colors of prickly pear fruit are the result of variations in betaxanthin and betacyanin contents. The betacianins pattern was dominated by betanin and the C15 diastereomer isobetanin as the principal red pigment while was the principal pigment of betaxanthins group in reddish purple fruit. On the other hand, indicaxanthin was the most characteristic betaxanthin compound found in the yellow cultivars. The presence of betanin and isobetanin and its 15R-isoform, were confirmed first by their identical spectral properties (maximum absorbance at 535 nm), secondly by the presence of their protonated molecular ions [M+H]+ with m/z 551, and lastly by the prominent secondary ion at m/z 389 due to the

1131 presence of the protonated aglycones [betanidin+H]+ or [isobetanidin+H]+. Both molecules differ only in the absolute configuration of their C15 chiral center. Gomphrenin I showed a different HPLC retention time compared to that of betanin, due to the difference in the attachment of the glucose at C-6 or C-5, respectively. Betanin eluted earlier than gomphrenin I. All betacyanins produced a daughter ion at m/z 389, corresponding to [betanidin+H]+. We have shown that indicaxanthin is the major betaxanthin compound in yellow, orange, red and purple colored prickly pear fruit. Interestingly, the yellow pulp of ‘21441’ showed the most complex HPLC profile. A variety of betaxanthins present in this cultivar provided information to identify most of the betaxanthins present in trace quantities in other cultivars. I, vulgaxanthin II, muscaaurin VII, miraxanthin II, serine Bx, were the most common betaxanthins present in the other yellow prickly pear fruit (Table 1). Betaxanthins were identified by comparison with the UV-vis and mass spectrometric characteristics as well as by comparison of retention times with those of semi-synthesized reference betaxanthins obtained according to a method described previously. The identities of all betaxanthin standards were checked by LC-MS analysis. Betanin, isobetanin, betanidin and isobetanidin were identified by comparison with the retention times of the respective betacyanins in an extract from red beet roots prepared as described previously. No reference compounds were available for the remaining betacyanins. Fruit of ‘Cardona’, ‘Roja Lisa’, ‘Naranjona’, ‘2142’ and ‘21441’ contain trace amounts of a new betacyanin identified as betanidin 5-O-(6′-O-malonyl)-β-sophoroside. To our knowledge this is the first time that this betacyanin is identified in prickly pear fruit. The identification was based on the molecular masses determined by HPLC-ESI-MS.

CONCLUSIONS Fruit of all cultivars/lines had a similar carotenoid profile, in which lutein was the most abundant compound in ‘Camuesa’ while neoxanthin was the most abundant compound in ‘21441’. Chlorophyll a was the most abundant form of chlorophyll in all cultivars/lines and the highest quantity was found in ‘Camuesa’. To our knowledge, this is the first time that identification of carotenoids and chlorophylls has been reported in prickly pear fruit using mass spectroscopy. Our study has confirmed that the variation in the content of the yellow-orange betaxanthins and the red-violet betacyanins as well as variations in the levels of certain structurally different betacyanins are responsible for the prickly pear fruit color, showing the potential value of prickly pear fruit, especially of the ‘Camuesa’ cultivar which showed the highest betalains content, as a good bioavailable source of pigments and their industrial exploitation for drinks and food products. Therefore, consumption of cactus pear fruit may provide nutritional and health benefit.

Literature Cited Piga, A. 2004. Cactus pear: a fruit of neutraceutical and functional importance. J. Prof. Assoc. Cactus 6:9-22. Stintzing, F.C., Herbach, K.M., Mosshammer, M.R., Carle, R., Yi, W., Sellappan, S., Akoh, C.C., Bunch, R. and Felker, P. 2005. Color, betalain pattern, and properties of cactus pear (Opuntia spp.) clones. J. Agric. Food Chem. 53:442-451. Stintzing, F.C., Schieber, A. and Carle, R. 2001. and nutritional significance of cactus pear. Eur. Food Res. Technol. 212:396-407. Yahia, E.M. 2009. Prickly pear Chapter 13. In: D. Rees, G. Farrell and J.E. Orchard (eds.), Crop postharvest: Science and Technology. Volume 3. Perishables. Willey- Blackwell Publishing, Oxford, UK. In press.

1132 Tables

Table 1. Qualitative and quantitative data of carotenoids and chlorophylls in fruit of ten prickly pear cultivars and lines by HPLC-ESI- MSa.

b Rt m/z Cultivar/line Peak Compound + Principal ions (min) [M+H] A B C D E F G H I J Carotenoid 1 All trans-neoxanthin 7.5 601 491[M+H-18-92], 221 tr tr tr tr tr tr tr tr tr tr 2 All trans-violaxanthin 8 601 583 [M+H-18], 565 [M+H-36], 221 tr tr tr tr tr tr tr tr tr tr 3 All cis-violaxanthin 11 601 583 [M+H-18], 221 tr tr tr tr tr tr tr tr tr tr 4 All cis-neoxanthin 11.5 601 583 [M+H-18], 393, 221 tr + + + + + + + + + 5 All trans-lutein 15.2 569 551 [M+H-18], 459 [M+H-18-92] ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ 7 not identified 15.2 795 549, 413 tr tr tr tr tr - - tr - tr 8 not identified 24.5 601 411, 397 + ------Chlorophyll 6 Chlorophyll A 17.8 893 871, 835, 593 + + + + tr + + + + + 9 Pheophytin A 25 871 593 + tr tr tr tr tr tr tr tr tr 10 Pheophytin B 25.5 901 851 tr tr tr tr tr tr tr tr tr tr a (++) present in moderate amount, (+) present in low amount; (tr) present in trace amounts, not quantified; (-) not detectable, that is, no mass signals could be obtained. (A) ‘Camuesa’, (B) ‘Roja pelota’, (C) ‘Cardona’, (D) ‘2142’, (E) ‘Liria’, (F) ‘Roja lisa’, (G) ‘Naranjona’, (H) ‘2651’, (I) ‘21441’, (J) ‘Reyna’. b Retention times of betalains according mass spectrometric data.

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Table 2. Chlorophyll a, and total chlorophylls in fruit of ten prickly pear cultivars.

Chlorophyll a Chlorophyll b Total chlorophylls (mg/100 g dry tissue) (mg/100 g dry tissue) (mg/100 g dry tissue) Camuesa 10.7 ± 0.22 4.8 ± 0.09 15.5 ± 0.31 Cardona 8.6 ± 0.24 3.9 ± 0.07 12.5 ± 0.31 2142 7.0 ± 0.01 3.0 ± 0.02 10.0 ± 0.04 Liria 6.4 ± 0.08 2.6 ± 0.03 9.0 ± 0.11 Roja Lisa 5.8 ± 0.24 2.6 ± 0.11 8.4 ± 0.35 Naranjona 5.4 ± 0.04 2.7 ± 0.00 8.0 ± 0.04 21441 4.2 ± 0.15 2.4 ± 0.06 6.6 ± 0.22 2651 4.1 ± 0.08 2.3 ± 0.04 6.4 ± 0.14 Roja Pelota 3.7 ± 0.24 2.1 ± 0.09 5.8 ± 0.33 Reina 3.6 ± 0.29 2.0 ± 0.18 5.6 ± 0.39 The results are the mean for three replicates ± standard error.

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Table 3. LC-MS data for betaxanthins and betacyanins contents in fruit of ten prickly pear cultivars and linesa

m/z Cultivar/line Trivial name Amino acid [M+H] trb + A B C D E F G H I J Betaxanthin Portulacaxanthin I Hydroxiproline 325 1.6 Tr Tr Tr + Portulacaxanthin III Glycine 269 1.8 Tr + Vulgaxanthin III Asparagine 326 5.1 TrTr Tr Muscaaurin Histidine 349 5.2 + + + + + Unknown Histidine derivative 305 6.5 + Unknown Serine 299 7.3 Tr + + + Vulgaxanthin I Glutamine 340 9.4 + + + Vulgaxanthin II Glutamic acid 341 14.5 Tr Tr Unknown γ-amino butiric acid 297 20.1 + Tr Tr Tr - TrTrTr+ - Unknown Proline isomer 309 21.0 + Tr TrTrTr Indicaxanthin Proline 309 22.0 ++++ + + Tr+ + + + - Unknown Methionine 329 27.2 + Tr Tr TrTrTr Unknown Valine 311 30.2 + Tr + + Tr Unknown Valine (isomer) 311 30.3 + Unknown Tryptophan 399 32.0 - Tr Unknown iso-leucine 325 33.9 Tr + Vulgaxanthin IV Leucine 325 34.1 + Tr Tr + Unknown Phenylalanine 359 34.4 + Tr Tr + + Tr Unknown Phenethylamine 315 36.0 Tr Tr TrTrTr Betacyanin Betanin 551 27.3 ++++++++++ + + + + Tr Iso-betanin 551 28.5 + + + + TrTrTr - Betanidin 389 27,28,30+ + + + + + + - Tr Tr Gomphrenin I 551 30.7 + + Tr + TrTr - - Tr - Neo-betanin 549 33.5 Tr Tr Tr Tr TrTr- - - - Unknown 459 34.07 Tr Tr + Tr TrTr- - a (+++) present in high amount, (++) present in moderate amount, (+ ) present in low amount; (Tr) present in trace amounts, not quantified; (-) not detectable, that is, no mass signals could be obtained. (A) ‘Camuesa’, (B) ‘Roja Pelota’, (C) ‘Cardona’, (D) ‘2142’, (E) ‘Liria’, (F) ‘Roja Lisa’, (G) ‘Naranjona’, (H) ‘2651’, (I) ‘21441’, (J) ‘Reina’. bRetention times of betalains according mass spectrometric data.

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Table 4. Betaxanthinsa, betacyaninsb and betalains contents in fruit of ten prickly pear cultivars and lines.

Betacyanins content Betaxanthins content Total Betalains Cultivar/line (mg/g dry pulp) (mg/g dry pulp ) (mg/g dry pulp) Water Buffer Water Buffer Water Buffer Camuesa 5.29 ± 0.35 5.01 ± 0.60 2.86 ± 0.24 2.56 ± 0.42 8.146 7.57 Roja Pelota 2.06 ± 0.06 1.86 ± 0.28 0.99 ± 0.03 0.84 ± 0.12 3.04 2.71 Cardona 2.04 ± 0.20 1.83 ± 0.00 1.04 ± 0.09 0.80 ± 0.00 3.08 2.63 2142 0.71 ± 0.04 0.66 ± 0.01 0.44 ± 0.03 0.38 ± 0.01 1.16 1.04 Liria 0.39 ± 0.03 0.34 ± 0.02 0.14 ± 0.01 0.11 ± 0.00 0.53 0.45 Roja Lisa 0.27 ± 0.01 0.22 ± 0.02 0.23 ± 0.02 0.18 ± 0.00 0.50 0.40 Naranjona 0.065 ± 0.01 0.04 ± 0.01 0.16 ± 0.02 0.12 ± 0.00 0.23 0.16 2651 0.072 ± 0.00 0.04 ± 0.01 0.14 ± 0.02 0.09 ± 0.01 0.21 0.13 21441 0.071 ± 0.00 0.05 ± 0.01 0.41 ± 0.02 0.35 ± 0.04 0.48 0.40 Reina 0.05 ± 0.02 0.03 ± 0.03 0.12 ± 0.01 0.23 ± 0.20 0.17 0.26 a,b The results are the mean for three replicates ± standard error.

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